Conventionally, in a building process in the manufacture of tires, there is known a building method in which for example, a cylindrical carcass band is built by affixing an inner liner made of a rubber material and carcass plies, which are a reinforcement member including a rubber chafer and cords, onto a circumferential surface of a building drum in such a manner as to lie on top of one on another, then, beads and sides are built into a green casing on a primary building drum, following this, the green casing is transferred on to a secondary shape deformable building drum so as to deform the green casing into a toroidal shape, and belts incorporating cords therein and tread rubber are affixed thereto to thereby build a green tire.
In addition, in recent years, there has also been proposed a method in which a carcass band and a belt/tread band which is made up of a carcass band and a belt and is adapted to be laid on the carcass band are built in separate steps in advance, and these band and belt/tread band are then combined together to be built up.
In implementing the building methods, the so-called belt building drum for building the belt/tread band is an expandable and contractible drum which is made up of a large number of segments which are divided in a circumferential direction, and when building a belt/tread band, the respective segments are held in such a state that they are expanded diametrically, and the respective members are affixed to the circumferential surface of the drum in such a manner as to lie on top of one on another to eventually build up the belt/tread band. Then, when removing the cylindrical belt/tread band so built for transfer to a subsequent step, the respective segments of the belt building drum are diametrically contracted in such a state the band is grabbed from an outer circumference thereof by a grabbing device of a transfer apparatus, whereby the removal of the band is implemented.
Because of this, in the belt building drum, a central shaft portion acting as a drum shaft is coupled to a motor acting as a rotating driving means of a driving apparatus, and the respective segments are coupled to an expanding/contracting driving means via an expanding/contracting mechanism.
As expanding/contracting mechanisms for building drums, various types of mechanisms such as those utilizing a cylinder device and a threaded shaft are adopted to cope with difference in type and building step of bands to be built.
As one of them, for example, in the case of a belt building drum, there is known a mechanism in which a threaded shaft is provided inside a cylindrical outer shaft which constitutes a central shaft portion of a building drum in such a manner as to rotate relative to the outer shaft, and a moving member which is thread fitted on the threaded shaft and respective segments are coupled together via a sloping guide such as a tapered cone or a linkage member, so that the moving member is moved in an axial direction by means of rotation of the threaded shaft, whereby the respective segments are operated to expand or contract.
In this case, as a driving device for the building drum, there are required a rotational driving means for rotating the outer shaft and a rotational driving means for rotating the threaded shaft for expanding/contracting operations. Motors are used as these rotational driving means.
Incidentally, when the drum is rotated for a belt and a tread rubber to be affixed together for building or to be pressed by a stitcher roller, the outer shaft and the inner threaded shaft need to synchronize to rotate in order to activate neither expanding operation nor contracting operation. However, in the event that the rotational driving means provided on the driving device for expanding/contracting operations, that is, the motor remains coupled to the threaded shaft, load against the rotation becomes large due to braking action by the motor, and a larger quantity of electric power becomes necessary by such an extent that the rotation is affected by the braking action, this being uneconomical.    Patent Document No. 1: JP-A-2003-89158